The present invention relates to a keyboard that drives a membrane switch by tactile-response collapsible or flip-over domes, and a method of making the keyboard.
A description will be given first, with reference to FIGS. 1 to 4, of a prior art example.
In FIG. 1, reference numeral 10 denotes a keyboard substrate made of a metal sheet or sheet of synthetic resin that has the same mechanical strength as does the metal sheet. Reference numeral 13 denotes a keyboard frame made of a metal sheet or sheet of synthetic resin that has the same mechanical strength as does the metal sheet. The substrate 10 has bumps 11 arranged in matrix form. The substrate 10 and the frame 13 overlying it are welded, fused or bonded together through the bumps 11 to define therebetween a gap in which to house a membrane switch sheet 20 described later on. Incidentally, the substrate 10 and the frame 13 are coupled together in the final step of the manufacturing process of the keyboard switch.
The frame 13 has, as depicted in FIGS. 3A and 4, punched-out openings 31 each corresponding to one of switch portions 20S of the membrane switch sheet 20 that are arranged in matrix form; hence, the openings 31 correspond to keytops 4, too). The membrane switch sheet 20, which is received in the gap defined by the substrate 10 and the frame 13, is composed of a movable contact sheet 21, a spacer 22 and a fixed contact sheet 23. The spacer 22 has punched-out contact areas 221. As depicted in FIG. 4, the movable contact sheet 21 has on the underside thereof a movable contact 211 and the fixed contact sheet 23 has on the top thereof a fixed contact 231 disposed opposite the movable contact 211. The contact area 221, the movable contact 211, the fixed contact 231 and the keytop 4, described later on, are positioned relative to one another to form the switch portion 20S. A plurality of such switch portions 20S are arranged in matrix form to provide the keyboard switch.
Reference numeral 4 denotes the keytop mentioned above. As shown in FIG. 1, the keytop 4 and the frame 13 are mechanically linked by a pantographic lifting or support frame 50 interposed therebetween. The pantographic support frame 50 has, as depicted in FIG. 2A, a first coupling rod 52, a pair of first links 5 each connected at one end to one of opposite ends of the first coupling rod 52 at right angles thereto and extending therefrom substantially in parallel with the other, a second coupling rod 63, and a pair of second links 6 each connected at one end to one of opposite ends of the second coupling rod 63 at right angles thereto and extending therefrom substantially in parallel with the other. The second links 6 are coupled together by a semicircular coupling portion 64 formed integrally therewith nearer their free ends than their centers so that an insertion hole 65 is defined by the coupling rod 63 and a semicircular coupling portion 64 for receiving a tactile-response collapsible dome. The first links 5 and the second links 6 are combined, with the outside surfaces of the latter intermediately of their ends held in contact with the inside surfaces of the central portions of the former intermediately of their ends. The first and second links 5 and 6 are connected centrally thereof by shafts 60 in a manner to be rotatable relative to each other as depicted in FIG. 1.
The keytop 4 has, as shown in FIG. 2B, on the underside thereof along its two opposed sides rotary bearings 41 and slide bearings 42. The coupling rod 52, which serves also as a keytop support rotary shaft of the first links 5, is rotatably received in the rotary bearings 41 of the keytop 4, whereas keytop support sliding shafts 62 of the second links 6 are slidably received in the slide bearings 42. As shown in FIGS. 1, 2A, 2B, 3A and 3B, leg slide shafts 51 of the first links 5 are slidably received in leg slide shaft bearings 32 formed by drawing the frame 13 in the vicinity of the switch portion 20S, and leg rotary shafts 61 of the second links 6 are rotatably received in leg rotary shaft bearings 33 formed by drawing the frame 13.
As depicted in FIG. 3A, the width D1 of the opening 31 between the leg slide shaft bearings 32 is smaller than the distance between the outermost ends of the leg slide shafts 51 but somewhat larger than the length of the connecting rod 52 so that the first links 5 and the rod 52 are allowed to pass through the opening 31. Accordingly, when the pantographic support frame 50 is mounted on the frame 13 with the leg rotary and slide shafts 61 and 51 received in the leg rotary and slide shaft bearings 33 and 32, respectively, in FIG. 4, the links 5 and 6 tilt toward the keytop 4 through the opening 31 and the keytop support rotary and slide shafts 52 and 62 engage the rotary and slide shaft bearings 41 and 42 on the underside of the keytop 4, respectively.
A tactile-response collapsible or flip-over dome 7 (FIGS. 1 and 2A) is composed of a cylindrical part 71 firmly fitted on a projection 43 formed on the underside of the keytop 4 centrally thereof, a dome part 72, a flange part 73 formed integrally with the lower end portion of the dome portion 72, and a press part 74 formed integrally with the ceiling of the dome portion 72. The dome 7 is made of rubber or elastic synthetic resin. The dome part 72 is elastically deformed by the cylindrical part 71 that is pressed down upon depression of the keytop 4, but the flange part 73 is formed thick and hence is not much deformed.
The dome 7 lies between the underside of the keytop 4 and the movable contact sheet 21 of the membrane switch sheet 20 through the opening 31 of the frame 13 and the dome insertion hole 65, holding the keytop 4 in its raised position. That is, if the dome 7 is not present, the pantographic support frame 50 is lowered and lies flat, but when the dome 7 is interposed between the underside of the keytop 4 and the movable contact sheet 21 of the membrane switch sheet 20, the keytop is pushed up by the dome 7 and the pantographic support frame 50 is raised almost its full height. The dome 7 has its cylindrical portion 71 engaged with the projection 43 (FIG. 1) protrusively provided on the underside of the keytop 4 centrally thereof as mentioned previously. The lower end face of the flange 73 is adhesive bonded to the surface of the movable contact sheet 31 in the vicinity of the opening 31 as indicated by 73.
Turning next to FIG. 4, the assembling of the keyboard will be described below. In FIG. 4 there are shown parts of only one key of the keyboard with their insides upward.
In the first place, keytops 4 with their undersides upward are arranged in matrix form on an assembly table (not shown) at intervals equal to those of the switch portions 20S. Then, the frame 13 is placed face down on the assembly table with each opening 31 held in alignment with the corresponding keytop 4. Then, the pantographic support frame 50 is placed with the keytop support slide shafts 62 engaged with the slide shaft bearings 42 and the coupling rod 52 also serving as the keytop support rotary shaft fitted in the slide shaft bearings 41, while at the same time the leg slide shafts 51 of the first links 5 are fitted in the leg slide shaft bearings 32 and the leg rotary shaft 61 of the second links 5 is fitted in the leg rotary shaft bearings 33. Then, the dome 7 with its cylindrical part 71 downward is inserted through the dome insertion hole 65 (FIG. 2A) and pressed to put the cylindrical part 71 on the projection 43 of the keytop 4. Then, an adhesive is applied onto the lower end face of the flange 73 of the dome 7. Then, the movable contact sheet 21 is placed on the frame 13 and the pantographic support frame 50 with the movable contact 11 upward opposite the dome 7. The assembling process is stopped until the adhesive sets, after which the spacer 22 is placed on the movable contact sheet 21 with the contact area 221 held in opposing relation to the movable contact 211. Then, the fixed contact sheet 23 is placed on the spacer 22 with the fixed contact 231 held opposite the contact area 221 of the spacer 22. Thereafter, the fixed contact sheet 23 is placed on the substrate 10, and the substrate 10 is welded to the frame 13 at the bumps 11 of the former. In this way, the keyboard is assembled.
Upon depression of the keytop 4, the dome 7 deforms with a tactile response and the press part 74 presses down the movable contact 211 into contact with the fixed contact 231. Upon releasing the pressure on the keytop 4, the dome 7 flips over and returns to its initial position, raising the press portion and hence allowing the movable contact 211 to get out of contact with the fixed contact 231.
In the above-described conventional keyboard, respective cylindrical parts 71 of usually as many as several tens of domes 7 are each engaged with the projection 43 on the underside of the corresponding keytop 4 and the lower end face of the flange part 73 is adhesive bonded to the movable contact sheet 21 in the neighborhood of the opening 31. The manufacture of this prior art example involves a step of adhesive bonding many domes 7 to the movable contact sheet 21xe2x80x94this makes the manufacturing process complicated and time-consuming. That is, the dome 7 is shown on an enlarged scale for convenience of description, but in practice it is so small that the diameter of the flange part 73 is as small as less than 4 mm. Accordingly, the step of adhesive bonding a large number of such miniature domes 7 to the movable contact sheet 21 involves many exacting tasks and consumes much time. In addition, the bonding step requires time for setting of the adhesive, and the keyboard assembling is inevitably discontinued and hence is inefficient.
Further, since the number of domes 7 to be adhesive bonded to the movable contact sheet 21 is so large that it is impossible to ensure good bonding of all the domes; that is, there is a case where some of them are not properly bonded to the sheet 21. Such improperly bonded domes need to be re-bonded after assembling of the keyboard, but this is very difficult to achieve. Incidentally, it is possible to avoid discontinuation of the assembling process by adhesive bonding the domes 7 on the surface of the movable contact sheet 21 prior to the start of the assembling. However, such a scheme also involves many exacting, time-consuming tasks, requires time for waiting for setting of the adhesive and suffers difficulties in re-bonding incorrectly bonded domes.
U.S. Pat. No. 5,967,298 discloses a keyboard free from such problems as mentioned above. In the U.S. patent a large diameter flange portion of the lower end portion of a dome is held on a substrate by a cylindrical member of a reduced diameter top end portion protrusively provided on the top of a flat frame, by which the dome is held on the substrate without using an adhesive. From its depicted configuration, it is estimated that the frame having formed integrally therewith the cylindrical member is formed by molding, though not mentioned specifically. In the case of forming the frame with such a cylindrical member by molding, it is difficult to make the thickness of the frame and the height of the cylindrical member small, inevitably making the keyboard thick.
It is therefore an object of the present invention to provide a keyboard that is free from the necessity for adhesive bonding tactile-response collapsible domes to the keyboard frame and hence is readily assembled and thin, and a method of making such a keyboard.
The keyboard according to the present invention comprises:
a membrane switch sheet on which there are switch portions are arranged in matrix form;
tactile-response collapsible domes each provided with a dome part having therein a press part for driving the corresponding one of the switch portions and a flange part formed around the lower end portion of the dome part, the dome parts being formed of an elastic rubber material and disposed on the membrane switch sheet in correspondence to the respective switch portions;
an embossed sheet in which there are formed embossed cylindrical protrusions each for receiving the flange part of the corresponding dome, the top end portion of each embossed cylindrical protrusion being reduced in diameter for engagement with the top end portion of the corresponding flange part and the embossed sheet being placed on the membrane switch sheet;
pantographic support frames disposed on the embossed sheet astride the tactile-response collapsible domes; and
keytops each mounted on one of the pantographic support frames and elastically biased upward by the top of the underlying tactile-response collapsible dome.
The keyboard manufacturing method according to the present invention comprises the steps of:
(a) placing a frame, which has openings each corresponding to one of keytops and rotary shaft bearings and slide shaft bearings formed around each opening, on the keytops held upside down and arranged in matrix form;
(b) disposing pantographic support frames on the opening of the frame in correspondence to the keytops, engaging keytop support slide shafts and a keytop support rotary shaft of each of the pantographic support frames with slide shaft bearings and rotary shaft bearings formed on the underside of each keytop and engaging leg slide shafts and leg rotary shafts of the pantographic support frame with the slide shaft bearings and rotary shaft bearings of the frame;
(c) placing on the back of the frame an embossed sheet in which embossed cylindrical protrusions each having a reduced diameter end portion are formed in correspondence to the keytops so that the embossed cylindrical protrusions each lie at the center of one of the pantographic support frame;
(d) inserting the top of each tactile-response collapsible dome into one of the embossed cylindrical protrusions from the back of the embossed sheet; and
(e) placing a membrane switch sheet, on which switch portions are formed in matrix form in correspondence to the keytops, on the back of the embossed sheet and fixing the membrane switch sheet to the frame.
In the keyboard and its manufacturing method according to the present invention, the embossed sheet need not always be used, but instead the embossed cylindrical protrusions may be formed in the frame.